A substrate transfer apparatus for automatically transferring substrates or a substrate container such as a cassette or carrier for storing the substrates in a semiconductor manufacturing apparatus or between semiconductor manufacturing apparatuses has been used to prevent foreign substances from attaching to plate-like substrates such as photomasks, reticles, wafers, or glass plates and to improve productivity.
In such a substrate transfer apparatus, a code having patterned substrate information is marked on a substrate or substrate container which contains substrates for better substrate management and operation in order to accurately identify and quickly feed a substrate such as a reticle required for each manufacturing step. The code is read in a substrate stocker, each step, or each apparatus to register and check the substrate.
To improve the reliability of management of substrates such as reticles, conventionally, a cassette and reticle are paired and managed by collating codes respectively marked on them, as disclosed in Japanese Patent Laid-Open No. 1-58859.
In such an apparatus, the material of a substrate such as a reticle is a transparent glass material, and a pattern used for exposure is formed at the central portion of the reticle. A code about reticle information is marked around this pattern. The pattern and code are made of chromium, and an antireflection film is formed on the surface of the pattern and code so as to prevent any adverse influence on exposure. The pattern and code have a low reflectance. When a general reflection reading method is used, the contrast between the pattern portion of the code and the reticle substrate is low, resulting in unstable reading.
In order to solve this problem, as disclosed in Japanese Patent Laid-Open No. 7-66118 and 10-149983, a transmission type reticle code reading apparatus is used in which a light-emitting portion is separated from a light-receiving portion. In reading the reticle code, a reticle is held on a transfer hand at a dedicated reading position when it is to be transferred from the reticle container to a processing section.
A conventional transmission type bar code reading method will be described with reference to FIGS. 12A and 12B. In FIGS. 12A and 12B, reference numeral 91 denotes a reticle made of a transparent glass material. A pattern portion 91b used for semiconductor exposure, alignment marks 91c used for various alignment operations in exposure and formed in the blank portion of the pattern portion 91b, and a bar code 91a serving as a reticle code are marked on the lower surface of the reticle 91 by using chromium or the like. Reference numeral 92 denotes a transfer hand for extracting the reticle 91 from a reticle carrier and transferring it to the exposure apparatus main body. The transfer hand 92 is horizontally and vertically movable by a driving device (not shown). Suction pads 92b for chucking the reticle by vacuum suction and reticle stoppers 92c for preventing any positional shift of the reticle are disposed on a pair of holding arms 92a of the transfer hand 92, respectively. A bar code reading unit 93 is comprised of an illumination portion 93a for illuminating the bar code on the reticle and a bar code reader 93b incorporating a light-receiving portion for reading the bar code. The bar code 91a of the reticle 91 read by the bar code reader 93b is converted into an electrical signal, which is sent to a terminal and used as a reticle ID to set various parameters in exposing the reticle.
In reading the bar code 91a, the reticle 91 is transferred to the reading position above the bar code reader 93b while being held by the transfer hand 92. At this time, the bar code 91a on the reticle 91 is positioned not to overlap the holding arms 92a of the transfer hand 92, as shown in FIG. 12B. At the reading position, light from the illumination portion 93a is partially shielded by the bar portions of the bar code 91a, which are made of chromium or the like, and forms a shadow on the detection portion of the bar code reader 93a. The space portions of the bar code 91a are the transparent glass portions of the reticle. The illumination light passes through the space portions, so that the bar code is projected on the detection portion of the bar code reader 93b. Therefore, the bar code 91a of the reticle 91 is read.
In recent years, an SMIF (Standardized Mechanical InterFace) reticle transfer system has been introduced. The SMIF reticle transfer system will be described below. An increase in foreign substance management level and a recent demand for high working efficiency so as to cope with a next gigabit generation inevitably increases the running cost of the equipment when the state-of-the-art cleaning scheme for cleaning the whole clean room by a downflow is employed. From this viewpoint, local cleaning of a clean space is required to propose the concept of a mini-environment represented by the SMIF, as proposed in Japanese Patent Publication No. 5-66733.
FIG. 10 is a schematic view showing a semiconductor exposure apparatus of a SMIF scheme having already been used in practice. FIGS. 11A to 11D are views illustrating reticle transport states in the SMIF semiconductor exposure apparatus.
The environment of the SMIF semiconductor exposure apparatus is equivalent to that of a chamber 60. The environment is separated from the environment outside the chamber in the clean room. The temperature, pressure, and cleanliness of the environment of the SMIF semiconductor exposure apparatus are managed. A plurality of load ports 61 are disposed on the horizontal portion of the chamber 60. A reticle SMIF pod 50 is placed on the load port 61 to load a reticle into the chamber 60. As shown in FIGS. 11A to 11D, the reticle SMIF pod 50 comprises a reticle carrier library 54 for storing a plurality of reticles 51, a carrier main body 52 and a pod door 53 for closing the lower opening of the carrier main body 52. The reticle SMIF pod 50 is set on the load port door 62 of the load port 61 (see FIG. 11B), and the pod door 53 is then unlocked by an unlocking mechanism incorporated in the load port door 62. As shown in FIG. 11C, the reticle carrier library 54, which stores the plurality of reticles 51, is extracted downward from the carrier main body 52 by an elevator mechanism 63 while the pod door 53 is held integrally with the load port door 62. The reticle carrier library 54 is loaded into the chamber 60. As shown in FIG. 11D, the reticles 51 stored in the reticle carrier library 54 can be loaded or unloaded by a reticle transfer robot 55 in the chamber 60. The reticle transfer robot 55 is comprised of a transfer hand 56 for chucking/holding a reticle, a robot main body 57 for driving the transfer hand 56, and a Z-axis driving unit 58 for vertically driving the robot main body 57.
In this SMIF scheme, assume that while one reticle is used in the apparatus, another reticle stored in the same carrier as the reticle used is to be used in another apparatus. In this case, the carrier is removed from the apparatus used. For this purpose, a reticle library (65 in FIG. 10) for storing a plurality of reticles is arranged to temporarily store the reticle currently used and to improve flexibility in reticle management.
In the conventional example described above, a reticle code is read with transmitted light on the transfer hand. In this case, however, since light does not pass through the holding arm which holds the reticle, no code is marked on a reticle portion vertically overlapping the holding arm. In addition, the reticle code must be formed so as not to interfere with alignment marks and the like. The position of the reticle code is limited, and the capacity of a substrate information code cannot be increased.
In the conventional example described above, when the reticle and cassette are managed in a pair, and the number of types of reticles increases as with ASICs, the number of cassettes increases accordingly to result in complex management. As a method not to manage the cassette and reticle in a pair, Japanese Patent Laid-Open No. 11-65093 discloses a method of directly reading a code on a reticle in a cassette. However, when a plurality of reticles are stored in one carrier as in the SMIF scheme or reticle codes of reticles in a reticle library are to be checked, it is impossible to read the codes marked around the patterns on the surfaces of reticles while the reticles are stored in the carrier because they are vertically stacked on each other at a small interval. In this case, a reticle is temporarily extracted from the reticle carrier and transferred to the dedicated code reading position, thereby reading the code. It takes a long time to read the code, resulting in inconvenience.